This invention relates to a fine pattern forming method using electron beam or focus ion beam lithography, and more particularly to a fine pattern forming method which is capable of enhancing dry-etch resistance of a resist by ion shower irradiation.
The fine pattern forming process is divided into lithography step and etching step. In order to enhance the dry-etch resistance of the resist pattern formed in the lithography step, it was attempted to improve the resistance of the resist material itself to dry etching by introducing phenyl radicals having a high dry-etch resistance in the resist component or using silicone resin. The dry-etch resistance was also increased by ion implantation after pattern forming.
On the other hand, in the lithography step, in order to form an image reversal pattern, baking or ammonia treatment is carried out, for example, as the treatment after exposure. By such image reversal process, a fine resist pattern will be obtained.
Thus, hitherto, various considerations were given to enhance the dry-etch resistance of the resist itself, but in order to form a fine pattern by raising the resolution, it is necessary to reduce the film thickness of resist. When etching the substance by using such fine pattern as the mask, since the resist itself is etched, it is difficult to transfer the pattern in the etching step when the film thickness is smaller. When attempting to enhance the dry-etch resistance by implanting ions into the resist pattern, ions are also implanted into the semiconductor substrate, and ion irradiation defects may occur.
Besides, in the conventional image reversal process, it can be applied only in a specific resist, and the dry-etch resistance was poor.